Help Hen has a large sac under her vent

I really need some help figuring out what is wrong with our Cochin hen. She has a large "sac" under her vent. We though she was egg bound but when trying to go in physically to get the egg our it was just soft and I can't seem to get to the "sac". I have posted pictures can someone tell me if it is egg bound or can it be a tumor?

Did you get any answers? One of our Buff Orps had the same thing. We just culled her and opened her up and it was yellow fatty ? Not sure if tissue is the correct term? I didn't see any eggs or yolks just this fatty yellow mass.